Okay so, an exponential functi0on is something that increases at a rate exponentially. So there is linear and exponential. They want to make it exponential so, since 3 times 2 equals 6, and we have to keep multiplying it by the same #, we would have to do 6 times 2 next.
That is 12. So I am assuming that r equals 12. If you wanted to do it arithmetically, 3 plus 3 is 6. so r would be 6+3. which is 9. But your answer to this question should be 12.